Insulating roll cover

ABSTRACT

An insulating roller cover is now disclosed that provides a highly desirable combination of features. The cover is free from asbestos and is therefore of more desirable construction for handling and use. For the roller cover, at least substantially ceramic fiber is highly compressed, providing a dense and refractory, elevated temperature resistant insulating cover. The cover may itself serve as a load bearing surface; or may provide a foundation or protective media for annular discs or 10 sleeve members made of various, load bearing materials. These load bearing materials may be unable to resist direct contact with the shaft due to thermal shock or the differences in their respective expansion and contraction rates. Where impregnant is utilized with the highly compressed fiber, such will often comprise a colloidal substituent.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional Ser. No. 08/361,502, filed Dec. 22,1994 now U.S. Pat. No. 5,709,639, which is a divisional patentapplication of Ser. No. 07/986,212, filed Dec. 7, 1992 (now U.S. Pat.No. 5,378,219) which is a divisional patent application of Ser. No.07/719,252, filed Jun. 27, 1991 (now U.S. Pat. No. 5,205,398) which is acontinuation-in-part of application Ser. No. 07/559,736, filed Jul. 27,1990, now abandoned.

BACKGROUND OF THE INVENTION

Rolls such as those employed as roller conveyors for use at hightemperature can be made from an inner metal shaft that has an outerinsulating cover of asbestos. In manufacturing the roll, the asbestoscan be supplied as annular discs, sometimes referred to as "washers",which are assembled on the shaft and pressed together, as discussed, forexample, in U.S. Pat. No. 3,802,495. In a technically related teachingin U.S. Pat. No. 3,116,053, there is disclosed a roll having asbestosdiscs compressed onto a tubular shaft, the asbestos discs alternatingbetween thick and thin discs.

These are pressed together between end walls by a compressive forceproduced by hydraulic means. Because the binding agent in the asbestostends to be destroyed at high temperature, it is important to maintainthe discs under the axial pressure between the end walls.

A conveyor roll can also be made by sliding a plurality of asbestosmillboard annular discs onto a shaft, i.e., annular discs of a majoramount of asbestos fiber and a minor amount of binder such as portlandcement. These can then be compressed axially on the shaft. As disclosedin U.S. Pat. No. 3,334,010 the asbestos can be a blend of chrysotileplus amphibole asbestos fibers and the binder can be a cement plus claymixture. In a somewhat technically related disclosure in U.S. Pat. No.3,456,931 it is discussed that the surface of the roll can be heated toproduce an exterior, ceramic surface on the roll.

It has also been proposed to make the discs from ceramic fiber board,having a binder such as portland cement. These discs can be assembled ona metal shaft and compressed into roller form. However, the binder has atendency to burn out, thus weakening the cover. Such covers havetherefore not met with wide acceptance as a suitable replacement for theasbestos millboard covers.

A proposal has also been made to use glassy fibers for rollers, such asrollers used in drawing sheet glass. In this regard, in U.S. Pat. No.3,763,533 it has been taught to impregnate mineral fiber with aninorganic binder. Strips of felted fiber can be wound around a rollercore, impregnated with binder and heated to dry. Such rolls have howevernot proven to be sufficiently acceptable to find wide use in replacingasbestos rollers.

It has also been proposed to use mineral fibers in feed rollers forroller tunnel kilns. U.S. Pat. No. 4,596,527 teaches the preparation offibrous tubes, or sleeves, which can be slipped over a feed-roller steelpipe core. These sleeves ostensibly assist in ease of rollermaintenance, as fresh sleeves can be readily slipped onto the pipe coreduring equipment down time after removal of the spent cover layer, whichseemingly is required frequently.

However, concerns over the safety of the working environment, as well asover potential damage to conveyed goods from fugitive binder residues atelevated roll use temperature, continues. There is still a need inindustry for an improved insulating roll covering, competitive inruggedness and long-service life with asbestos covers. Such roll covershould also exhibit desirable insulating characteristic, yet provide amore environmentally safe product by elimination of asbestos.

SUMMARY OF THE INVENTION

There is now manufactured an improved insulating roll cover. Theresulting roller not only has an insulating cover, but such a coverwhich can offer improved insulating property over even prior asbestoscovers. Yet the cover is asbestos free for more desirable handling anduse. Furthermore, the cover may be free of binders such as cement,thereby eliminating problems with such covers. The new roller canthereby offer the desirable features found in previous insulatingrollers, while combining these features with much sought afterimprovements.

In a broad aspect the invention is directed to a roller especiallyadapted for use in roller conveying articles, which articles are atsubstantially elevated temperature, or which articles are being conveyedthrough a zone of substantially elevated temperature, which rollercomprises an inner shaft having at least one dense and refractory,elevated temperature resistant annular insulating cover member of highlycompressed at least substantially ceramic fiber.

In another aspect the invention relates to an insulating cover memberwherein the compressed fiber includes fibers that are compressed in anamount within the range of from about 50 percent to about 80 percent toa density within the range of from about 16 to about 50 pounds per cubicfoot.

In still another aspect the invention is directed to a highly compressedfiber, as above described, as a new composition of matter. Other aspectsof the invention are directed to the method of making an insulating rollcover, to the roll covers of the present invention which may containadditive for hardening the cover and to their method of manufacture.Still further invention aspects are directed to novel roll covers havingthe highly compressed fiber as an underlayer, or core, for an outerlayer of refractory which can be a fiber-containing material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an insulating roll having a centralshaft and fiber cover.

FIG. 2 is a view in section, a portion only, of an insulating roll ofthe present invention, the roll being a double-type roll variationcontaining a load bearing member in the cover and having a castableoutermost layer.

FIG. 3 is a partial view, in section, of an insulating roll of thepresent invention depicting a double type roll variation.

FIG. 4 is also a partial view, in section, of an insulating roll of thepresent invention having a hardcoat outer layer.

FIG. 5 is an exploded view depicting the assembly of fiber discs intofiber sections and then into roll cover preparation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the roller, at least one roller cover insulating layer will beprovided by highly compressed, at least substantially ceramic fiber. Itis often advantageous that this fiber be binder-free. Compressed,binder-containing fiber may be useful, and will be discussed further onhereinbelow. By "at least substantially ceramic fiber" it is meant thatthe fiber will be a major amount, i.e., greater than 50 weight percent,of ceramic fiber. The minor amount, i.e., under 50 weight percent,balance can be other synthetic or natural mineral fiber, e.g., glassfiber or mineral wool, including mineral wool with additives.Advantageously, for best roller performance without degradation underhigh heat application, the fiber will be at least about 80 weightpercent ceramic fiber and preferably for best overall performancecharacteristics, will be all ceramic fiber.

Although it is contemplated that such ceramic fiber may not be asilica-containing fiber, as represented by alumina fiber or fiber ofboron compound material, e.g., fibers of boron oxide, boron carbide andboron nitride, it is preferred for economy that the ceramic fiber be asilica-containing fiber. The silica-containing fiber may simply besilica fiber, although usually the silica is present with one or more ofalumina, zirconia, chromia, or titania. Such silica-containing fibersare also meant to include fibers from silicon nitride, silicon carbide,calcium-aluminum silicate and the like. Advantageous fibers which havedesirable inertness, i.e., non-reactivity with the working environmentas well as with articles being conveyed over the roller, combined with adesirable insulating property can be prepared from silica and alumina.Improved high-temperature properties for ceramic fiber can be achievedwhen the silica and alumina are combined with zirconia or titania.

Typically, with commercially available fibers prepared from silica andalumina, the alumina content can vary in an amount of from about 45 toabout 80 weight percent alumina with an about 20 to 55 weight percentbalance of silica. Where additional substituents are utilized, e.g.,zirconia, the constituent ranges can be further varied. Thus wherezirconia may be present, it might contribute as little as about 3 weightpercent. There can then be present, as taught in U.S. Pat. Nos.4,558,015 and 4,555,492, silica in an amount from about 45 up to 75weight percent or more, and alumina in an amount of as little as about10 weight percent, up to nearly 40 weight percent. Moreover, the amountof zirconia in some formulations may exceed 20 weight percent. It willbe understood that the fiber may be prepared by any process useful forpreparing ceramic fiber. Commercially, such processes include thosewhich fiberize a molten stream, e.g., blowing of a molten stream tofiberize the molten material, or causing the molten stream to impactrapidly spinning wheels which fiberizes the melt. Commercial manufacturealso includes sol-gel processing.

As the fibers are produced, it will be typical that they will beinitially accumulated together into a mat form. Such may be accomplishedas by collecting random fibers on a continuous chain-mesh beltapparatus. The accumulated fibers that typically are collected on themesh belt apparatus can then be needled or stitched together. Forpurposes of the present invention, these fibers in mat form, or whenconsolidated as by needling into blankets, can also be compressed, withor without the application of heat. Typically in accumulated form, theinitial mats will have a density on the order of from about 2 to about 4pounds per cubic foot, and after consolidating the fiber, theaccumulated fibers as blankets will have a density on the order of fromabout 4 to 10 pounds per cubic foot for ceramic fiber. Anyprecompression in accumulating the fibers, as by heating or rolling,will still typically provide a blanket having a density of not aboveabout 10 pounds per cubic foot.

The mats or blankets, the fiber in which may also be generally referredto herein as "bulk" fiber, can be stamped or cut into disc shape.Bundles of these discs, especially when stamped from a thin blanket, maythen be precompressed into multiple-disc "sections" sometimes alsoreferred to herein as "donuts". Typically, the initial blankets can havethickness from on the order of 1/4 to 1/2 inch, up to as thick as 6inches. For the thinner ceramic fiber blankets which are usually 1/4inch up to about 1 inch thick, discs can be compressed into typically 1inch to 4 inch thick sections. The thicker blanket discs may not beprecompressed into sections. Upon compression into sections, whichcompression can be in an amount, as more particularly discussedhereinbelow, from about 50 percent to about 80 percent, the fiber may becompressed to a density that might vary, in broadest consideration andbasis dry fiber, within the range of from about 16 to about 50 poundsper cubic foot.

As an example, a blanket prepared from a readily available commercialsilica-alumina fiber and having an initial density, as formed, of 8pounds per cubic foot, or "18-pound blanket", can be compressed 50percent to a density of 16 pounds per cubic foot. More typically, fiberwill be compressed to provide a density within the range of from about18 to about 40 pounds per cubic foot. The same readily availablecommercial fiber 8-pound blanket compressed above about 60 percent canprovide a fiber density of on the order of greater than 20 pounds percubic foot. If compressed more toward the top of the range, e.g., 80percent, such 8-pound blanket will have density approaching 40 poundsper cubic foot. For such commercial ceramic fiber prepared from silicaand alumina, a greater than 20 pounds per cubic foot density, e.g., anabout 22 to 40 pound per cubic foot range of density, is highlyadvantageous for best fiber insulating characteristic. It is to beunderstood that compression may be of wet or dry fiber, but unlessotherwise specified, compressed fiber densities are to be understood tobe for dry fiber.

For many applications it is most advantageous to utilize a bulk fibersince the individual fibers in the bulk fiber are of varying lengths.Such fibers of varying lengths enhance the ability of the fibers tointertwine and hold together under compression. For these applicationsusing fibers of varying lengths, it is further desirable that all fibershave a length of at least about 0.5 inch, with long fibers usuallyhaving length within the range of from about 8 inches up to a length ofabout 10 inches. Usually only a very few fibers will be longer thanabout 10 inches, as such fibers can be difficult to work with, whilefibers shorter than about 0.5 inch may be of insufficient length toeffectively intertwine for these fibers of varying lengths. Aparticularly preferred fiber mixture for fibers of varying lengths hassome individual short fibers at least about 2 to 4 inches long, inmixture with long fibers, i.e., longer than 4 inches and with lengths upto about 8 to 10 inches, often with fibers of at least about 6 to 8inches in length.

It is however to be understood that in some applications it can beuseful to employ milled fiber or chopped fiber, or both. Chopped fiberi.e., bulk fiber which has been chopped, can have individual fibersgenerally from 0.25 inch to one inch in length. Milled fiber, typicallyfiber that has been chopped and subsequently ball-milled, can be ofextremely short, and more uniform length. Fiber lengths for milled fibercan be on the order of 10 to 30 microns. Although mixtures arecontemplated for milled fiber with other fibers, e.g., one or more ofchopped fibers or the above described fibers of varying lengths, it isto be understood that the milled fiber may be utilized by itself, suchas in a hardcoat formulation, as will be described in detailhereinafter. Also, since milled fiber is not as subject to fibercrushing as are individual longer length fibers, the utilization ofmilled fiber can be particularly serviceable at elevated ,,compression.

Milled fiber may be used in applications in rollers where elevated shotcontent, or shot of enlarged size, or both, may be deleterious, such asrollers utilized with stainless steel strip in catenary lines where shotcan lead to marking of the product. As the word is used herein, "shot"refers to the non-fibrous, and usually chunky, ceramic particles thatare found in bulk ceramic fiber, e.g., ceramic fiber blanket. Typically,where long fibers that have individual fibers of varying lengths areused, the shot content retained on a 40 mesh screen (U.S. Sieve Series)may be as great as on the order of 2 to 5 percent, with particle sizefor individual pieces of the shot being as great as 100 microns. If suchis of concern, a castable cover, more typically a hardcoat cover, asdepicted in FIG. 2 and discussed hereinbelow, can be used as a shotcontainment coating. Also, use of milled fiber may enhance rollerserviceability, since milling of the fiber tends to crush shot particlesto a size of less than about 20 microns, thus reducing to eliminatingconcern for product marking. Chopped fiber can be similarly utilized inthe manner of milled fiber, such as in mixture. Alone or in mixture itcan be most serviceable in castable formulations such as in a shotcontainment coating. It can thus be especially useful where marking ofthe articles being conveyed across the roller is of concern.

It has not been industrial convention to substantially compress ceramicfiber owing to a concern for crushing the fiber. It has however now beenfound that discs of the fiber on a shaft can be highly axiallycompressed. Such compression for ceramic fiber should be in an amountfrom above about 50 percent up to most always about 80 percent, althoughslightly greater compression, i.e., 83 to 85 percent might be achieved.A compression of less than about 50 percent will not provide for adesirable dense fiber having the requisite resistance to compression atthe roll surface as required in the industry. On the other hand, mostalways a compression of greater than about 80 percent may lead to fibercrushing. Advantageously for desirable roll strength and resistance tosurface compression, the ceramic fiber will be compressed in an amountabove about 55 percent, or more often above about 60 percent andpreferably within a range of from about 65 to about 75 percent.

The amount of compression tolerated by the fiber without deleteriousfiber crushing may be determined by the wet or dry condition of thefiber. In fiber production, the fiber can usually be expected to be indry condition, and appear and feel dry to the touch, often owing to theelevated temperature conditions used in producing the fiber. In brief,wet fiber is fiber that has been wetted, such as with a lubricant,rigidizer or binder, each of which will be discussed hereinbelow, andthe fiber can appear and feel wet to the touch. As a general rule, wetfiber can be more highly compressed without running as great a risk offiber crushing. With dry fiber, a range of compression for ceramic fiberfrom above about 50 percent up to about 70 percent or possibly, as amost elevated compression, about 75 percent, will be advantageous. It isgenerally contemplated that wet fiber will be readily susceptible tocompression across the full 50 percent to 80 percent compression range.However, even with wet fiber, compression from about 50 percent, up toabout 70 percent, is preferred. By wet fiber, it is meant to includefiber which is simply wetted by water. More typically, a lubricant willbe used. By use of the word "lubricant" herein there is meant the use ofa substituent which will volatilize without providing more than anincidental residue in the roller, and preferably, no residue. Suchvolatilization will most always be complete at drying temperature,although some residual volatilization may be effected at the operatingtemperature of the roller. Generally, the lubricants are organicmaterials including organic liquids or organic substituents dispersed orsolubilized in liquids. Soap dispersions can serve as useful lubricants.The lubricant can be applied to the fiber when the fiber is in mat form,by any means usually employed for applying a liquid to a porous solid,e.g., spray or dip application. It also may by useful to apply thelubricant to a disc or section that has been partially compressed. Thelubricant can penetrate into the partially compressed fiber mass, as bywicking. The resulting lubricated fiber mass is then subjected to finalcompression.

For some applications it may be desirable to use a binder in thecompressed fiber roll cover. Such may be a "fugitive binder", that is, abinder that will be readily susceptible to volatilization from the coverduring drying of the cover or at elevated temperature use. Such fugitivebinder may readily penetrate into the compressed fiber roll. It may alsobe referred to herein as an "organic binder", and representative suchbinders include starch, latex materials and cellulosic substituents,e.g., an aqueous suspension of cellulose methyl ether. The word "binder"may also refer to a substance which will not readily penetrate into thecompressed fiber roll, such as by wicking, in appreciable amount. Thesebinders, sometimes referred to herein as "inorganic binders", in generalmay be used with the fiber prior to or after compression. Representativeinorganic binders include cements, calcium aluminate and clays. Thus,the inorganic binders are materials which will be present, at least as aresidue in substantial amount, in the compressed fiber roll cover duringuse of the roll cover.

If the material used is capable of impregnating the compressed fiberroll, i.e., wicking into the compressed fiber roll, as well as alsoleaving a residue within the roll on drying and which will be retainedin the roll for roller use, such material is referred to herein forconvenience as a "rigidizer". Representative rigidizers are such ascolloidal silica, colloidal alumina, colloidal zirconia, or similarliquid materials. Where the rigidizer used is in colloidal form, it maybe referred to herein as a "colloidal rigidizer". The rigidizer may beapplied to the fiber either before compression or after. The method usedmay be any of those typically employed for impregnating a fiber with aliquid, e.g., soaking or spraying or the like. Even for the most highlycompressed fiber, i.e., the 80 percent fiber compression, a rigidizermixture, e.g., a solution containing colloidal silica or colloidalalumina or both in a liquid vehicle, will readily impregnate the rollcover by capillary action, or "wicking", and can penetrate completelythroughout the compressed ceramic fiber. It is however to be understoodthat such penetration may purposefully be limited to only an outermostlayer of the compressed ceramic fiber, or that the impregnation willprovide a gradation of the rigidizer, which can be most concentrated atthe outer roller fiber surface.

Generally, the rigidizer composition will include colloidal silica suchas a LUDOXR colloidal silica dispersion manufactured by E. I. DuPont deNemours and Company. Such dispersions are understood to be aqueoussuspensions of sodium-stabilized, or ammonia or aluminum stabilized,silica particles, with ammonia stabilized being preferred, typicallycontaining 40-50 weight percent solids, but may be more dilute, e.g.,contain 20 weight percent solids. The colloidal silicas, which may alsobe referred to herein as silica sols, are generally the alkaline sols,e.g., having a pH of at least 8.5. They are understood to be composed ofdiscrete dense spherical particles typically of silica. Suitablesubstitutes for silica in sol form can include ethyl silicates, silicatepolymers, ethyl polysilicates and colloidal alumina such as aluminumoxide sol. It is to be understood that where a rigidizer compositionsuch as a silica sol is to be used, such can be further modified tocontain additional additives. These additives may include on the orderof from as little as 0.1 weight percent of up to 5 weight percent ormore, e.g., up to 10 weight percent, basis the weight of the rigidizercomposition solids, of an additive such as an organosilane couplingagent, or a polymeric agent such as an acrylic polymer. It is alsocontemplated that compressing and rigidizing can be a multi-stepprocess. For example a fiber roll may be compressed, e.g., at 50 percentcompression, then penetrated with a rigidizer, then compressed further,as by up to as much as 80 percent. Additional rigidizer could then beadded after the second compression step. Moreover, whenever therigidizer is used, it can be used in a multi-step,impregnate-dry-impregnate operation terminating in a final drying step.

Generally, the rigidizer will be used in an amount to provide from about5 weight percent up to about 70 weight percent or more, and preferablyabout 15 to 60 weight percent, of rigidizer residue after drying of theroll, in the total weight of the roll. After use, the resultingimpregnated cover should be dried. Drying, as such term will generallybe used herein, may be accomplished at quite elevated temperature, e.g.,500° C., but also such for economy will advantageously be at a moremodest temperature such as from about 300° C. down to about 100° C. orbelow. After application of rigidizer, drying is preferably at such moremodest temperature, e.g., about 200° C., for a time of up to about 24hours, but more usually from about 8 hours to about 12 hours.Thereafter, the fiber cover may be further conditioned in a manner suchas described hereinbelow. For example, the cover can be heat treated atan elevated temperature of as much as up to about 2000° F. for animpregnated ceramic fiber, thereby vaporizing any fugitive solvent orliquid vehicle of a rigidizer or of a binder and leaving the residue inthe compressed fiber roll cover;

Referring then to the figures, FIG. 1 shows a roll 1 comprised of ametal shaft 2 having a compressed fiber cover 3. The compressed fibercover 3 is contained within end plates 4. The metal shaft 2 is supportedand may be internally cooled all by means not shown. The end plates 4maintain compression on the compressed fiber cover 3, also by means notshown.

Referring then to FIG. 2, a roll 10 has an inner shaft 11. This shaft 11may be solid, but in the figure is depicted as hollow providing apassageway 12 for entry of a cooling liquid feeding from a source notshown into the shaft 11. At the zone of the shaft 11 over which objectswill be conveyed, the passageway 12 expands into a cooling chamber 13.At the end opposite from the cooling chamber 13, the shaft is supportedand may be rotationally driven, all by means not shown. The outerportion of the metal shaft 11 is substantially covered along the axialdirection of the shaft 11 with an inner core member 14 of compressedfiber discs. This fiber disc inner core member 14 can be held undercompression by means of an end stud 41 which has an outer threadedsurface 42. On top of the fiber disc inner core member 14 is an outercover member 16 of compressed ceramic fiber discs. For maintaining endplate compressive pressure on the outer cover member 16 there is used apush ring 43 and threaded nut 44. Interspersed between these compressedfiber discs of this outer cover member 16 axially along the inner coremember 14, is a load bearing member 17. This member is cushioned by theinner core member 14 and firmed in place by the outer cover member 16,which also permits for expansion and contraction of the load bearingmember 17. The load bearing member 17 has an exterior surface 18. On theouter surface of the outer cover member 16 of compressed fiber discs isan outermost castable cover layer 19, which may also be referred toherein as a "shot containment coating". This outermost cover layer 19can serve to contain shot in the outer cover member 16, if such ispresent. It is to be understood that these load bearing members 17, willhave their exterior surface 18 raised above the castable cover layer 19,as for example in application where the roller 10 is used for conveyingstrip steel to a catenary furnace for annealing.

Referring next to FIG. 3 a roll 10 has a shaft 11, which is hollow,providing a passageway 12 for a cooling liquid. At the end of the roll10 there is an end plate 15 secured by welding to the shaft 11. Forinsulation, this roll 10 has an inner, compressed fiber roll cover 31prepared from compressed fiber discs (not shown), which inner cover 31is compressed in direct contact with the metal shaft 11. Although thisinner roll cover 31 will be referred to herein as the compressed fiberroll cover 31, it is to be understood that for some covers the innerroll may be obtained in a manner other than the compression discussedherein, e.g., by vacuum forming. On top of this inner, compressed fiberroll cover 31 is an outer compressed fiber roll cover 32. Thisparticular roll construction of FIGS. 2 and 3, which may be referred toherein as a "double-type" roll, contains, for example, the inner rollcover 31 and the outer roll cover 32, of FIG. 3. Covers of suchstructure will be discussed again hereinbelow. Contained in the outercompressed fiber roll cover 32 is a load bearing member 17. This loadbearing member 17 has an exterior surface 18 which is shown flush withthe outer surface of the outer compressed fiber roll cover 32. This loadbearing member 17 inwardly in a radial direction is seated on the innerroll cover 31. Additionally, it is to be understood that suchdouble-type roll may initially have only compressed fiber for the outerroll cover 32. Then, a groove can be machined in this outer roll cover32 and castable material is then cast or placed in the groove to serveas the load bearing member 17.

Referring then to FIG. 4, a roll 10 has a metal shaft 11 which containsa passageway 12 for a cooling liquid, not shown. At the end of the shaft11 there is an end plate 15 secured to the shaft 11 by welding. Mounteddirectly on the outer surface of the shaft 11 is a compressed fiber rollcover 36 prepared from compressed fiber discs (not shown). Atop thiscompressed fiber roll cover 36 is an outer hardcoat layer 37. Hardcoatsas will be serviceable for preparing such a hardcoat layer 37 arediscussed in greater detail hereinafter. Also present around the metalshaft 11 are spacers 38. As depicted in the figure, the spacer 38extends through the compressed fiber roll cover 36 as well as thehardcoat layer 37. This spacer 38 can serve to add flexibility to thecovering for the roll 10. Although the spacers 38 may take the generalform of a load bearing member 17, they are however not load bearingmembers. The spacers 38 may be flush with, recessed, or raised above theouter surface of the compressed fiber. Suitable materials for suchspacers include ceramic fiber board and fibers in accumulated form,especially those which have been made by the sol-gel process, as well asmetals in foil form, e.g., foil discs, with each separator being acompressed product of multiple, individual metal foil discs.

As depicted in FIG. 4, only the compressed fiber roll cover 36 abutsagainst the end plate 15. This not only maintains compression for thefiber roll cover 36, but also maintains placement for the spacer 38. Inthe assembly depicted, the hardcoat layer 37 is thus not under axialcompression. Also, for a double-type roll, as depicted in FIG. 2, thestud 41 abutting against only the inner core 14 may be in fixedposition. Then the outer cover 16 is compressed against the push ring 43and under adjustable compression from the threaded nut 44. In thismanner, the inner roll cover 14 and outer roll cover 16 can bemaintained under differing compression. Understandably, at the oppositeend of the roll the end plate may be the same for both the inner coremember 14 and outer cover member 16, and may be fixed, as the weldedplate 15 of FIG. 3. The nut 44 of FIG. 2, can then permit adjustablecompression for the outer cover member 16, which compression may beadjusted during use of the roll 10.

Referring then to FIG. 5, a representative fiber disc 21, such as aneedled disc of silica-containing ceramic fiber, is accumulated with asubstantial additional number of like discs 21. By use of the term"disc" herein it is meant an object of most usually circular outerdiameter, although it is to be understood that the disc may be ofdiffering shape. For example, the disc may be oval or out of round toprovide a cam affect, or possibly contain edges or ridges, such as toprovide a ratchet affect. In this regard then, it is contemplated thatthe outer parameter will most always ascribe a substantially circularconfiguration. The disc 21 has an at least substantially centrallylocated disc aperture 22. Typically the disc 21 will have an aperture22, in this case circular, that has an aperture dimension, in this casea diameter dimension, that extends within the range from about 0.5 inchto about 8 inches. However, other aperture shape, such as hexagonal, maybe useful whereby the aperture dimension will be across the center ofthe disc from flat-to-flat.

As discussed hereinbefore, these discs, which are precompressed intosections, will typically have a thickness axially of at least about 1/4inch usually to about 1 or 2 inches, although discs of axial thicknessof as great as 8 inches are contemplated. It is to be understood thatespecially for these discs 21 of greater axial thickness, such may beprecompressed even before they are compressed into sections 23. Usuallythere will be a width of fiber, measured outwardly, from the center ofthe discs 21 of at least about 1 inch, and can be up to about 4 to 6inches, or more, e.g., 12 inches, extending from the outer edge of thedisc aperture 22 to the outermost perimeter of the disc 21. Suchoutermost perimeter will generally extend, as measured by the length ofa line through the center of the disc 21, from about 2 inches to about 3feet, which generally because of the preferred circular shape of thedisc 21 will be referred to herein as a diameter of from about 2 inchesto about 3 feet.

A bunch of these fiber discs 21 which are usually of lesser blanketthickness are then compressed to provide a fiber section 23. Such afiber section 23 can be prepared from the fiber discs 21 by compressingthe discs 21. This compression can be undertaken by any means generallyuseful for compressing fiber, e.g., by the use of air or hydraulicpressure. Although precompressing of fiber sections will almost alwaysbe handled on the shaft, it is to be understood that sometimescompressed fiber sections will be otherwise formed and then placed onthe shaft. The fiber section 23 will usually be compressed in an amountfrom about 50 percent to about 80 percent to provide a fiber densitywithin the range from about 16 to about 50 pounds per cubic foot. Theresulting fiber sections 23 are then at least substantially similar inshape to the fiber discs 21, e.g., have a section aperture 24 dimensionas well as total section diameter dimension as for the disc 21. Asmentioned hereinabove, these precompressed sections 23 will have axialthickness typically within the range from about 1 inch to about 4inches, although they may be much thicker, e.g., up to almost 2 feet.The use of adhesives or other means to prepare these sections 23 isoften avoided. When such are avoided, the resulting roll cover may becompletely additive-free in use.

The sections 23 are then accumulated onto a metal shaft 25 by simplysliding the section 23 over the shaft 25 so that the shaft passesthrough the aperture 24. The shaft 25 at its far end is equipped with anend plate 26. Typically, the metal shaft 25 will have a hollow, at leastsubstantially centrally located aperture 27 which can be used for thepassage of cooling fluid, not shown. When a substantial number ofsections 23, e.g. on the order of a dozen or more, have been assembledin a loose pack on the shaft 25, a moveable end plate, not shown, ismoved against the last-on section 23 in a manner opposing the end plate26. Pressure can then be brought on the fiber sections 23 by the endplates in any manner convenient for compressing the fiber sectionstogether. For example, threaded rods can connect the end plates and anair wrench can be used to tighten bolts at the end of the rods togradually bring the end plates closer and closer together. Or hydrauliccylinders can be used to press against end plates, thereby obviating theneed for threaded rods. After compression of the sections 23 by suchprocedure, a locking ring, not shown, can be used to replace the movableend plate and the procedure can be repeated of sliding an assembly offiber sections 23 onto the shaft 25 with the subsequent reapplication ofthe movable end plate and then applying pressure. It is to be understoodthat for the discs 21, and particularly for discs 21 prepared fromthicker blanket, e.g., blanket on the order of from about 4 inches to 6inches thick, that such discs 21 can be placed directly on the shaft 25.Pressure will be brought against these discs without need forprecompression into sections. When a roll 28 of desired length has beenassembled, the movable end plate can be replaced by a permanent endplate. It is contemplated that any hard, high temperature resistantmaterial may serve for the central shaft 25, e.g., a ceramic or metalshaft such as an iron shaft. The material should also be non-porous andliquid confining if a hollow shaft is used along with a coolant.However, for economy the shaft will most always be a metal shaft andadvantageously for best economy a steel shaft. Where internal cooling isemployed, such can be accomplished by means of a circulating fluid,which for economy is preferably water or air. It is well recognized thatthese shafts in use can warp, particularly under upset conditions. Theouter coverings with their insulating character, thus desirably enhancethe service life of the roll. Although the shafts herein have all beenshown to be circular in cross-section, it is to be understood that otherforms, e.g., square or hexagonal, can also be useful.

Where load bearing members 17 are used, which members 17 may also bereferred to herein as "tires", these can be made from any hightemperature resistant, as well as shrinkage resistant, and hard materialsuch as a ceramic or metal. It is important that such load bearingmember 17 be capable of accepting and maintaining a smooth exteriorsurface 18. Many materials can or have been used for these load bearingmembers 17 in industry. However, it is most usual to manufacture theseload bearing members 17 of ceramic material such as a silica. Fusedsilica is resistant to shrinkage and has virtually no coefficient ofexpansion under the typical operating conditions of the roll. Thesecharacteristics make fused silica particularly attractive for thisapplication. Other materials that may be used include steel, mullite,fiber board, cordierite or other castable material in addition to thejust discussed fused silica, hardcoat and binder.

It should be understood that in addition to using fused silica or thelike, e.g., alumina or zirconia or combination including such materials,as a load bearing member 17, such is representative of materials whichalso may be utilized as a sleeve. By use of the word "sleeve", it ismeant an item that can be slid over some to all of the outer surface ofthe compressed fiber cover. U.S. Pat. No. 3,751,195 discusses a sleeveof fused silica particles interbonded with colloidal silica or cement.It is to be understood that the fused silica sleeve material of thispatent may be cast directly on an underlying compressed fiber layer andcured thereon. Whether employed as a sleeve, or as a tire, or whetherdirectly cast on underlying fiber, the fused silica or the like willserve to extend the wear life of the roll, since the sleeve bears theweight of objects that are being transported over the roll. Such asleeve, or tire (load bearing member), or direct cast material, can beprepared from a composition which will generally be referred to hereinas a "castable" material.

As the term is used herein, "castable" material means any material whichcan be hardened to form a load bearing sleeve or tire, or such materialcured directly on an underlying compressed fiber layer. The material canbe cast directly over the compressed ceramic fiber roll cover, such asto provide an outer cover wear tread. Thus, particularly for suchmaterial, radial compression may be used with such roll, or at leastconstraint can be used in a radial direction, as where the material iscast over the ceramic fiber. However, it will be understood that ingeneral the ceramic fiber will be subjected to axial compression,although it is contemplated that a combination of axial compression withradial compression, or constraint, may be used. In addition to includingceramics such as fused silica, such castable materials may typically bemade from formulations containing silicates, e.g., sodium silicate orzirconium silicate, in combination with oxides, such as aluminum oxideor magnesium oxide, as well as be typically made from cermets, or fromcement or clay, which might be in mixture with additional ingredientssuch as ceramic fiber and talc. Where the material specifically includesa rigidizer plus ceramic fiber, usually chopped fiber or milled fiber,or both, which material is typically cast on underlying compressedfiber, this specie of castable material will most always be referred toherein for convenience as a "hardcoat". Such a hardcoat provides aparticularly desirable shot containment coating 19 as depicted in FIG.2.

For example, U.S. Pat. No. 4,174,331 discloses a hardcoat compositioncomprising ceramic fiber, silica and an adhesion agent such as anacrylic polymer or cellulose material. As formulated, a preferredhardcoat can contain milled ceramic fiber, usually in a major weightamount for the hardcoat fibers, and chopped ceramic fiber in minorweight amount. Some additional fibers, e.g., carbon fiber may also bepresent. Such preferred hardcoat may contain from about 70 to about 95weight percent, and more often 75-85 weight percent, of milled fiber, 5to 25 weight percent, and most always 13-23 weight percent, of choppedfiber and a balance up to about 5 weight percent carbon fiber. Usuallythere will be on the order of about 2 weight percent or less of carbonfiber in this preferred composition. Since the carbon fiber may burn outas the formulation is dried, the retained hardcoat composition may thencontain the other fibers in slightly differing amount, e.g., more on theorder of about a 75 weight percent minimum for milled fiber. In thiscomposition, it is desirable to have the milled fiber be prepared by aprocess which fiberizes a molten stream, and then have the chopped fiberprepared by the sol-gel process. For such preferred hardcoat, therigidizer used will be a colloidal rigidizer. In formulating thehardcoat, this colloidal rigidizer will advantageously contribute fromabout 20 to about 60 weight percent of the hardcoat compositionformulation, basis a rigidizer of 40 weight percent solids. Hence, suchrigidizer can be expected to provide an about 8-24 weight percent ofsolids in the dry hardcoat. Preferably, the colloidal rigidizer will bepresent in an amount from about 30 to about 50 weight percent of suchwet formulation.

A castable composition of particular interest includes rigidizer pluschopped ceramic fiber together with binder. More particularly, therigidizer employed will be colloidal rigidizer. Typically, the rigidizerwill supply from about 20 weight percent to about 60 weight percent ofthe total wet formulation, i.e., about 8 to 24 weight percent of thefinal product, solids basis, for a 40 weight percent solids colloidalrigidizer. More often, the rigidizer will supply from about 30 to about50 weight percent of the formulation. Another substantial ingredientwill be chopped ceramic fiber. Usually this will be fiber prepared bythe sol-gel process. This fiber may be present in the final solidproduct in an amount from about 20 to about 40 weight percent of thetotal formulation. Then a binder such as calcium aluminate can bepresent in an amount from about 35 to about 60 weight percent of theformulation. Frequently a combination of binder ingredients will beused, e.g., calcium aluminate with talc. In such instances, the secondbinder ingredient, i.e., the talc, will typically supply about 5 weightpercent of the total formulation.

After such a roll 28 has been freshly assembled, the outer surface ofthe roll may be rough. It can then be worked to provide a hardened, aswell as smooth, outer roll fiber surface. For example, the outer surfaceof the ceramic fiber can be smoothed by burnishing the fiber, usuallyafter machining, or after machining plus grinding. This may be achievedby forcing a highly polished rotatable metal element forcefully againstthe fiber surface and then moving this burnishing tool back and forthagainst the fiber roll as the fiber roll is being rotated. Smoothing cannot only provide for a highly desirable smooth and uniform surface, butcan also serve to improve and harden the fiber cover at its outersurface. This outer surface working can also be utilized to provideindentations in the fiber cover, e.g., so as to provide a textured outerappearance that can serve to offer better gripping of the cover with theproduct moving across the roll cover. After any outer surface working,including machining or grinding, the fiber cover may then be furtherconditioned, e.g., heat treated as by laser annealing, at an elevatedtemperature such as within the range of from about 1000° F. to about2000° F. for ceramic fiber. Such heat treatment may be performed beforeor after working, e.g., burnishing. Advantageously for economy, no suchfurther conditioning .is generally necessary.

The fiber cover, without using rigidizer or binder, and without an outersleeve or layer of castable material, will provide a dense, impactresistant and thermally stable surface. Moreover, the super compressedcover now achieved can exhibit minimal shrinkage in use, e.g., on theorder of merely 2 to 4 percent or less. This minimal shrinkage willdesirably retard, and can even eliminate, the separation of individualcompressed fiber discs during roll use.

The compressed fiber cover, without using rigidizer or binder, willtypically not register hardness on testing with a Schmidt hammer, whichmay also be referred to herein as an "H-Meter". Thus for someapplications it will be desirable to use rigidizer or binder in thecompressed fiber cover to obtain a more hardened surface. For example, acommercial silica and alumina ceramic fiber of intertwined varyinglength fibers, and compressed to about 60% compression can have enhancedsurface hardness by rigidizer application. For a single application ofrigidizer to such fiber, or "single dip", the compressed fiber rollsurface after drying will usually have a surface hardness within therange of from about 10 to about 20, as measured by Schmidt hammer usingthe R scale in a range of 1,500 to 10,000 pounds per square inch. Where,after drying, the resulting rigidized fiber is subjected to a secondapplication of rigidizer, also termed "double dipping", the hardenedsurface, after drying, will typically have a surface hardness within therange of from about 20 up to about 40, as measured by Schmidt hammer.Additional dipping is also contemplated, with drying between eachdipping operation. Thus, the compressed fiber roll cover lends itselfwell to adjustment of surface hardness by rigidizer application, andthereby lends itself well to tailoring the surface hardness for theparticular industrial use of the ceramic fiber roller.

As has been noted hereinabove, particularly in connection with FIG. 3,the roll cover may have an inner, more flexible core covering the rollershaft, with an outer, more rigid outer cover. This may be achieved withan inner, compressed fiber core. It is to be understood that this innerfiber core may be a wrapped fiber core, achieved as by wrapping stripsof blanket around the shaft. This core may be compressed as by radialcompression for a wrapped fiber core, or axial compression for a fibercore from discs. Compression for the core can be reduced compression,e.g., compressed at below about 60 percent. Such inner core may or maynot contain one or more of lubricant, binder, or rigidizer. On this moreflexible core there can be fabricated or placed a sleeve, as discussedhereinabove. Such also might be a more highly compressed fiber, e.g.,compressed above about 60 percent, or a highly compressed fibercontaining rigidizer or binder, or both. Particularly where the outercover member is highly compressed fiber, it is to be understood thatsuch may be used over a variety of core materials, e.g., including fiberboard materials. In the service, the outer cover member may even serveas a recap on a commercial roller, including used rollers. Suchmanufacture will then combine the desirable heat insulationcharacteristic for both the inner and outer members, which may becombined with flexibility offered by the inner core, coupled with adesirable wear surface for the outer member.

The following examples show ways in which the invention has beenpracticed. However, these examples should not be construed as limitingthe invention.

EXAMPLE 1

A commercial ceramic fiber, prepared by the blown melt fiberizing of amolten stream of a melt composed of 56 percent alumina and a balanceessentially silica, is consolidated into blanket form by needling. Theblanket contains fibers of varying lengths including short fibers havinglengths from on the order of from 2 to 4 inches together with longfibers having length up to 10 inches. The fiber is 8-pound blankethaving a thickness of one inch. This blanket is used to prepare discs bystamping discs from the blanket. The discs have a six inches outerdiameter and a 3 1/16 inch inner diameter over the flats of a hexagonalshaft. Thereafter 278 of these discs are accumulated onto the shaft,using 1/4 of the discs for each disc section. The steel hexagonal shafthas a 3 inch outer diameter over the flats and was hollow for aircooling. The initial 1/4 section of discs is compressed against a fixedend plate for the roll, such as depicted in FIG. 5, at a pressure ofabout 65 percent. This section is then locked on the shaft and thesecond 1/4 section of discs is compressed at about 65 percent on theshaft and locked. After all 4 sections were similarly compressed, theresulting roll had an axial compressed cover length along the roll of 927/8 inches.

The resulting dry cover was then dipped in a 40 percent solids silicasol (Nalco 2327, Nalco Chemical Company) for a 45 minute soak.Afterwards the roll was dried for about 8 hours at 200° F. This same dipand dry procedure was repeated a second time, but the roll was dried for12 hours at 300° F. The roll was then turned, i.e., machined for initialsmoothing of the roll surface, then grinding to complete this operation,resulting in a roll having an outer roll diameter of 5 3/16 inches.

This roll, plus a companion roll manufactured in the same manner, werethen installed as a bottom pair of rolls in a vertical glass drawingmachine containing 18 pairs of rolls. In this application, the rollersproceeded for over two months of commercial operation, free from anydeleterious cracking or shrinkage, thereby demonstrating serviceabilityfor these rolls in this application.

EXAMPLE 2

The commercial ceramic fiber employed was as described in Example 1. The8-pound blanket from this fiber, having one inch thickness, was used toprepare discs by stamping. The discs had a 6 inches outer diameter and a4 inches inner diameter. Thereafter, in the manner described in Example1, a total of 180 of these discs are accumulated onto a shaft to providea resulting roll having an axial compressed cover length along the rollof 60 inches. The shaft was a steel shaft, which was round in shapehaving a 4 inches outer diameter and was hollow for air or watercooling. Processing to this point provided an inner core of compressedceramic fiber discs.

The outer core of ceramic fiber was likewise prepared from 8-poundblanket discs having one inch thickness. These discs for the outer coverhad a 10 inches outer diameter and a 6 inches inner diameter to fit overthe inner core. These outer cover discs were likewise compressed, andover the inner core, but after each quarter of the discs, a tire wasinserted along with the outer discs, thereby providing three tires forthe roll. Both mullite and cordierite tires were used. The tires had a10 1/2 inches outer diameter and a 6 inches inner diameter. They alsohad a 1 1/2 inch width. As shown in FIG. 2, upon completion ofcompression of the outer ring, a steel push ring is placed against theend of the compressed outer fibers and a threaded nut is then tightenedagainst the steel push ring to maintain the axial compression on thisouter fiber ring. After completion of this outer cover, the resultingroll had an axial compressed cover length, including the three tires, of60 inches.

There was thereafter cast onto the outer cover a hardcoat layer. Duringcoating, the outer surfaces of the tires were masked with pressuresensitive tape. The hardcoat employed was a commercial adhesive cementcontaining sodium silicate and aluminum oxide and available fromSauereisen-Cements. This composition was cast onto the cover by pouringthe hardcoat onto the cover and smoothing by hand toweling. Theresulting hardcoat cover was then dried at 300° F. for 12 hours. Theresulting roller, with water cooling, then proceeded through 24 hours oftest operation. In the test, the roll was continuously rotated in afurnace at a temperature of 1600° F. for 12 hours and then 2200° F. for12 hours. After such testing, this double-layer roll with hardcoat outerlayer and load bearing tires, was judged to be a highly-serviceableroll.

We claim:
 1. A ceramic fiber disc of accumulated ceramic fiber, saiddisc having an axial thickness of at least about 0.25 inch, with therebeing an inner aperture for said disc having an aperture dimensionextending within the range from about 0.5 inch to about 8 inches, andwith there being at least about 1 inch of accumulated ceramic fiberextending from the outer perimeter of said aperture to the outerperimeter of said disc, with said outer perimeter of said disc having adiameter within the range from about two inches to about 3 feet.
 2. Theceramic fiber disc of claim 1, wherein said accumulated fiber is needledor stitched in blanket form.
 3. The ceramic fiber disc of claim 1,wherein said accumulated fiber has a density within the range of fromabout 4 to about 10 pounds per cubic foot.
 4. The ceramic fiber disc ofclaim 1, wherein said fiber comprises silica-containing ceramic fiber ofsilica with one or more of alumina, zirconia, chromia, or titania. 5.The ceramic fiber disc of claim 1, wherein said silica-containing fiberis a mixture of fibers having length of at least about 0.5 inch andincludes individual short fibers having a length within the range offrom about 2 inches to about 4 inches, together with individual longfibers having a length up to about 10 inches.
 6. The ceramic fiber discof claim 1, wherein said disc has axial thickness of up to about 8inches, with there being up to about 12 inches of fiber from the outerperimeter of said aperture to the outer perimeter of said disc.
 7. Theceramic fiber disc of claim 1, wherein said disc comprises accumulatedfiber plus rigidizer.
 8. A roll cover comprising highly compressedceramic fiber discs of claim
 1. 9. The roll cover of claim 8 whereinsaid highly compressed ceramic fiber discs comprise compressed fiberplus one or more of colloidal silica, colloidal alumina, colloidalzirconia or silane.
 10. A ceramic fiber section having an axialthickness within the range from about 1 inch to about 2 feet, with therebeing an inner aperture for said section having an aperture dimensionwithin the range from about 0.5 inch to about 8 inches, and with therebeing at least about 1 inch of ceramic fiber extending from saidaperture outwardly to an outer perimeter surface, with said sectionhaving an overall diameter to said outer perimeter surface within therange from about 2 inches to about 3 feet, said fiber being compressedin an amount from about 50 percent to about 80 percent to provide afiber density, basis dry fiber, within the range from about 16 to about50 pounds per cubic foot.
 11. The ceramic fiber section of claim 10,wherein said fiber comprises silica-containing ceramic fiber of silicawith one or more of alumina, zirconia, chromia, or titania.
 12. Theceramic fiber section of claim 11, wherein silica-containing fiber is amixture of fibers having length of at least about 0.5 inch and includesindividual short fibers having a length within the range of from about 2inches to about 4 inches together with individual long fibers having alength up to about 10 inches.
 13. The ceramic fiber section of claim 11,wherein said section has axial thickness of up to about 8 inches, withthere being up to about 12 inches of fiber from the outer perimeter ofsaid aperture to the outer perimeter of said section.
 14. The ceramicfiber section of claim 11, wherein said section comprises compressedceramic fiber plus rigidizer.
 15. The ceramic fiber section of claim 11,wherein said compressed fiber is dry fiber compressed in an amountwithin the range of from about 55 percent to about 65 percent and has adensity within the range of from about 18 to about 25 pounds per cubicfoot.
 16. The ceramic fiber section of claim 11, wherein said compressedfiber is wet fiber compressed in an amount of from greater than 60percent up to about 80 percent and has a density, basis dry fiber,within the range of from about 20 to about 40 pounds per cubic foot. 17.A roll cover comprising highly compressed ceramic fiber sections ofclaim
 11. 18. The roll cover of claim 17 wherein said highly compressedceramic fiber sections comprise compressed fiber plus one or more ofcolloidal silica, colloidal alumina, colloidal zirconia or silane.